Electrolysis apparatus



Dec. 11, 1956 NEWCQMBE 2,773,825

ELECTROLYSIS APPARATUS Filed April 28. 1944 ATTORNEY United States Patent ELECTROLYSIS APPARATUS Frank A. Newcombe, Nutley, N. J., assignor to the United States of America as represented by the United States Atomic Energy Commission Application April 28, 1944, Serial No. 533,110

2 Claims. 01. 204-243 This invention relates to apparatus for the recovery of rare refractory metals by electrolysis, and more particularly to furnace and crucible structures for the electrolysis of uranium halides in a fused salt mixture.

In the recovery of rare refractory metals such as uranium and thorium by the electrodeposition of such metals from metal salts in fused electrolytes, it has been found desirable to use carbon or graphite crucibles or cells because of the high temperatures required and because of the chemical activity of the materials processed. Methods for the electrolytic recovery of uranium are disclosed in the copending application of William C. Lilliend'ahl et aL, Serial No. 478,270, filed March 6, 1943, now United States Letters Patent No. 2,690,421, dated September 28, 1954. Briefly, the methods disclosed in said copending application include the electrolysis of uranium halides, such as potassium uranousfiuoride,

KUF5, uranium tetrachloride, UCiA, or uranium tetraw fluoride, UF4, in a fused electrolyte of calcium and sodium chlorides, whereby uranium in the form of 'a powder is electrodeposited on a cathode. The present invention relates to improvements in furnaces and crucibles or cells particularly suitable for use in the methods described in said application and in similar processes.

The ditficulties involved in the recovery of rare refractory metals by electrolysis are due to the relatively high operating temperatures required, and also to the chemical activity of the halogen compounds processed. The electrolytic recovery of uranium from uranium salts in a fused mixture of alkali or alkaline earth metal halides is conducted preferably at temperatures in excess of 800 C. in order to obtain the deposition of uranium powder of desired grain size, and the use of such temperatures presents difiiculties by reason of the fact that electrolysis at these temperatures causes chlorine and fluorine gases to .be evolved and may cause some of the fused salts to vaporize. These gases and vapors attack and corrode the electrolysis apparatus. The vapors condense on exposed portions of the electrolysis furnace and crucible, and both gases and salts tend to seep into the heating furnace where they attack the crucible holding means, the heating devices, and the electrolysis current connections generally provided. 'The damage and delays caused by corrosion and premature burning out of heating coil windings must be avoided in commercial production plants.

It has been found that excellent results may be obtained byusing graphite crucibles or cells, provided with suitable protecting seals at the exposed open end, and by having a protected anode connection at the base of the crucible. 4 It has also been found that the upper edges of the crucible should be somewhat above the level of the molten electrolyte in order to provide a graphite sur face on which vapors may condense. It is also advantageous to have the electrolysis crucible readily removable from the, electrolysis furnace in order that the crucible may be quickly replaced, and the electrolysis 2,773,825 Patented Dec. 11, 1956 operations carried on with a minimum of delays and interruptions.

It is an object of this invention to provide an electrolysis furnace and crucible construction adapted for eflicient operation in the electrolytic recovery of rare refractory metals.

It is another object of this invention to provide an electrolysis furnace and crucible construction in which the crucible is readily removable from the furnace structure for replacement.

It is a further object of this invention to provide an electrolysis furnace and crucible construction in which the various parts and electrical connections are protected from the deleterious effects of the vapors, gases, and salts present in high temperature electrolysis methods.

It is a further object of this invention to provide a refractory seal for an electrolysis furnace and crucible construction to prevent access. of the crucible contents to the surrounding furnace structure.

It is a further object of this invention to provide a graphite electrolysis crucible having an anode electrical connection thereto at the bottom of the crucible that is protected from the heat and contents of the crucible.

Other objects and advantages of this invention will be readily apparent to those skilled in the art from the following description of preferred embodiments of the invention illustrated in the accompanying drawings, in which:

Fig. 1 is an elevational view partly in section of an electrolysis furnace and crucible construction. Figs. 2, 3, and 4 are elevational views partly in section of preferred forms of electrical connections for crucibles that may be used in the apparatus, illustrated in Fig. 1, and show only a portion of the electrolysis crucible. Fig. 5 is an elevational view in section of a portion of the electrolysis furnace and crucible construction showing a modified form thereof.

Referring to the construction illustrated in Fig. 1, the base of an electrolysis furnace is indicated by the numeral 10. The furnace may be contained or enclosed by sides 11 and a top 12, the base, sides, and top being constructed from Transite or other heat-resisting sheet material. A rigid sleeve or pot 13 is positioned within the central portion of the furnace and may be supported from the base 10 by any suitable means such as a ring 14. The sleeve 13 is provided with a central opening aligned with the ring 14, and both the sleeve and the ring may be of Alundum or cast iron or the like. The base 10 is provided with a central opening in the bottom thereof. An electrolysis crucible or cell 15 of electrical conducting material preferably carbon or graphite, is positioned in the sleeve 13 with enough clearance to provide for easy withdrawal of the crucible for replacement.

The sleeve 13 may be provided with a resistance heating coil 16 wound in grooves on its outer surface, the coil being provided with suitable leads 17 and 18 to connect it to a source of electricity. Where an iron sleeve is used, the Winding 16 should be insulated therefrom. Other heating means such as a high frequency induction coil or glow bars may be used in place of coil 16 for heating the crucible 15. The numeral 19 designates a cathode electrode of any known type extending into a fused salt electrolyte 20 contained in the crucible 15. The interior space of the furnace between the walls 11 and the sleeve 13 and ring 14 may be filled with insulating material 21, such as magnesia or Silocel.

In the construction shown in Fig. 1, the anode electrical connection to the crucible 15 is effected by a threaded silver-plated copper plug 22 connected to the bottom surface of the crucible by a threaded bushing 23 of graphite. The plug 22 extends outward through the central opening in the base and may project several inches below the furnace base. A positive electrical connection to the plug 22 may be made by a copper clamp or conductor 24, which may also be a cooling coil, wrapped and/ or clamped or soldered to the projecting portion of electrode 22.

A ring member 25 of angular cross section extends around the outer surface of sleeve 13 near the upper end thereof for supporting sealing material 26 between the ring 25 and the furnace top 12. The sealing material 26 may be a refractory graphite cement and functions to prevent the passage of vapors, gases, or salts into the furnace insulation 21 and/ or onto the heating coil .16 on the outer surface of sleeve 13. A graphite healing material 27 may be used to fill or close at the top the space between the crucible 1S and the sleeve 13 to prevent vapors, gases, or salts from attacking the inner surface of sleeve 13 or the positive connection.

The mode of operation of the construction illustrated in Fig. 1 will now be described. In accordance with the methods disclosed in the above-mentioned copending Lilliendahl et al., application, a mixture of calcium chloride and sodium chloride is placed in the crucible 15. The mixture 20 is heated and fused by means of the heating coil 16 which elevates the temperature of the fused mixture to temperatures approximately 900 C. A rare refractory metal salt, such as potassium uranium fluoride, KUFs, uranium chloride, UCl4, or uranium fluoride UF4, is added to the fused mixture 20 and the cathode 19 and the plug 22 are connected to a suitable source of direct current. While the electrolysis is taking place, the current provides enough heat to keep the mixture 20 molten, and the heating coil 16 may be disconnected. The electrolysis causes the decomposition of the rare refractory metal salt in the fused mixture 20, and the rare refractory metal deposits as a powder on the cathode 19. The cathode electrode 39 may be withdrawn and replaced whenever sufiicient metal has been electrodeposited there The electrolysis process causes chlorine and fluorine gases and vaporized salts to be given off by the fused mixture 20. These vaporized salts tend to condense on the exposed upper portions of the crucible 15 and seep into the surrounding furnace structure. The sealing material 26 supported by ring effectively prevents this, since the gases, vapors, and salts emanating from the electrolysis crucible 15 are precluded thereby from reaching the heating coil 16, the external surface of sleeve 13, and the heat insulating material 21, with the result that the life of these parts of the furnace is substantially prolonged. The sealing material 27 between the crucible 15 and the sleeve 13 likewise prevents gases, vapors, and salts from the crucible 15 from contacting the interior surface of the sleeve 13 and the anode bushing 23 and plug 22.

Referring now to Fig. 2, the bottom portion of an electrolysis crucible or cell is designated by the numeral 39. In this construction, a plug 31 is connected to the crucible 30 by a threaded connection 32. The plug 31 is preferably of copper and may be silver-plated to reduce corrosion where it comes in contact with the crucible 30. This type of a connection is similar to that shown in Fig. l, but docs not require a bushing between the crucible and the plug. The construction shown in Fig. 2 may be substituted for that shown in Fig. l, and the mode of operation is similar to that described in connection with the apparatus of Fig. 1.

In the construction illustrated in Fig. 3, the plug 33 is made integral with the bottom of the graphite crucible 34. This construction minimizes a possible voltage drop in the electrical connection to the crucible. The plug 33 is machined from the crucible material 34 to the proper size to carry the total current flow desired in the electrolysis operation.

The modified construction shown in Fig. 4 eliminates the use of a threaded connection between the crucible 35 and the connection 36, the latter being provided with an 4 enlarged head 37 which makes a surface to surface contact with the bottom of the crucible 35.

Any of the anode electrode connections shown in Figs. 2, 3 and 4 may be used in place of the anode electrode construction shown in Fig. 1 as will be apparent to those skilled in the art.

The structure illustrated in Fig. 5 shows a modified form of seal for the upper edge of the electrolysis crucible. Referring to Fig. 5, the carbon or graphite crucible 40 is positioned in a supporting sleeve or cup 41 of iron or Alundum. Graphite filler material may be placed in the space between the crucible 40 and the sleeve 41 to prevent fused salts and vapors from getting into this space as previously described. A machined graphite ring 42 rests on the upper end of the crucible 40, being fitted thereto with an annular tongue and groove joint 43. The head of the ring 42 extends over the edge of the furnace top 44 to prevent the seepage of salts and vapors from the crucible 40 into the enclosing furnace. A cathode electrode 19, as in the construction of Fig. 1 extends into the crucible 40. Likewise, the sleeve 41 may be provided with a resistance heating coil 16 or other heating means and be surrounded by insulating material 21. It is to be understood that the construction shown in Fig. 5 may be embodied in the furnace construction shown in Fig. 1, and that crucible 40 may be provided with an anode electrode construction such as the bushing 23 and plug 22 shown in Fig. l, the threaded plug 31 shown in Fig. 2, the integral electrode 33 shown in Fig. 3, or the contact connection 36 of the construction shown in Fig. 4.

The furnace and crucible construction shown and described has been found to be particularly suitable in overcoming the diificulties involved in the electrolytic production of uranium from a fused mixture of uranium salt and alkali and alkaline earth metal halides. The improved construction provides for efficient electrical connection to a high temperature electrolysis cell or crucible, and also provides against damage to the electrical connections and to the furnace parts by chemical attack. The improved construction provides a relatively long life for the furnace and crucible and permits quick replacement of the crucible for substantially continuous operation of the electrolysis apparatus.

Numerous variations and modifications in the preferred forms of apparatus described will be readily apparent and may be made without departing from the spirit and scope of my invention as defined in the following claims.

I claim:

i. In apparatus for the recovery of uranium metal by electrodeposition thereof on a cathode insertable therein, the combination comprising a container, heat insulating material lining said container, 9. ring supported by said container, a rigid sleeve positioned in said insulating material and supported on said ring, an electrical heating coil surrounding said sleeve, a graphite crucible for receiving an electrolyte containing a uranium salt, said crucible being positioned in and spaced from said sleeve, graphite sealing means intermediate the sleeve and the crucible, a rod of conducting material projecting downwardly from said crucible to provide an anode connection for said crucible, and a cooling coil surrounding said rod and establishing a thermal and electrical connection therewith.

2. In an apparatus for the recovery of uranium metal by electrodeposition thereof on a cathode insertable therein, the combination comprising a container, heat insulating material lining said container, a ring supported by said container, a rigid sleeve positioned in said insulating material and supported on said ring, an electrical heating coil surrounding said sleeve, a second ring of angular cross section secured to said sleeve adjacent the top thereof, an annular furnace top within said container and resting upon the heat insulating material, graphite sealing cement supported on said second ring'and in sealing contact with said furnace top, a graphite crucible for receiving an electrolyte containing a uranium salt positioned in and spaced trom said sleeve, graphite sealing means intermediate the sleeve and the crucible, a rod of conducting material projecting downwardly from said crucible to provide an anode connection for said crucible, and a cooling coil surrounding said rod and establishing a thermal and electrical connect-ion therewith.

References Cited in the file of this patent UNITED STATES PATENTS 6 Ashcroft Jan. 12, 1926 Heany Apr. 25, 1933 Gadeau Mar. 17, 1936 Hulse Sept. 20, 1938 Lowry Dec. 15, 1942 Miner Apr. 13, 1943 Fox Mar. 21, 1944 FOREIGN PATENTS Great Britain Oct. 11, 1897 Great Britain Sept. 11, 1936 Australia June 8, 1939 Great Britain Ian. 30, 1942 

1. IN APPARATUS FOR THE RECOVERY OF URANIUM METAL BY ELECTRODEPOSITION THEREOF ON A CATHODE INSERTABLE THEREIN, THE COMBINATION COMPRISING A CONTAINER, HEAT INSULATING MATERIAL LINING SAID CONTAINER, A RING SUPPORTED BY SAID CONTAINER, A RIGID SLEEVE POSITIONED IN SAID INSULATING MATERIAL AND SUPPORTED ON SAID RING, AN ELECTRICAL HEATING COIL SURROUNDING SAID SLEEVE, A GRAPHITE, CRUCIBLE FOR RECEIVING AN ELCTROLYTE CONTAINING A URANIUM SALT, SAID CRUCIBLE BEING POSITIONED IN AND SPACED FROM SAID SLEEVE, GRAPHITE SEALING MEANS INTERMEDIATE THE SLEEVE AND THE CRUCIBLE, A ROD OF CONDUCTING MATERIAL PROJECTING DOWNWARDLY FROM SAID CRUCIBLE TO PROVIDE AN ANODE CONNECTION FOR SAID CRUCIBLE, AND A COOLING COIL SURROUNDING SAID ROD AND ESTABLISHIG A THERMAL AND ELECTRICAL CONNECTION THEREWITH. 